Energy gap of the superconducting semiconductor SrTiO3−x determined by tunneling

Binnig, G.; Hoenig, H. E.

doi:10.1016/0038-1098(74)91020-5

Cited by 29 publications

(10 citation statements)

References 17 publications

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“…The temperature dependence of the local pair binding energy  deduced from the excitation gap has been also studied in diamond and silicon, and found in excellent agreement with a s-wave BCS superconductivity with a BCS ratio /kBTC = 1.75 both for a C:B plate 140 and C(100):B epilayers 123,139 , while a 20% dispersion about the BCS value was observed 143 on Si:B. Two coupled gaps had been detected earlier in SrTiO3, with a BCS ratio close to 1.76 for the larger one 96 , as well as a possible signature of the soft phonon mode at 1.9 meV involved in the low temperature structural transition 138 . Moreover, optical methods have yielded superconducting gap values for C(111):B, infrared and THz spectroscopies 116 appearing to be better suited than high resolution photoemission 109 for the purpose.…”

Section: D Superconducting Propertiesmentioning

confidence: 81%

“…Since the pioneering tunnel spectroscopy studies 16 of GeTe, the superconducting gap of energy seen by the quasiparticles around the Fermi level has been investigated in 96,138 SrTiO3 , in 139 C(100):B, in 140 C:B, in 141,142 C(111):B and 143 Si:B. Thanks to the development of ultra-low T scanning tunnel microscopy (STM) and spectroscopy (STS), the latter studies have provided local maps of the local variations of the coherence peak intensity and of the superconducting gap 139,142,143 .…”

Section: D Superconducting Propertiesmentioning

confidence: 99%

“…The lines correspond to TC estimates for three µ* values, as deduced from equation 1 for D = 640 K,  being evaluated by ab-initio supercell calculations 41 . [139][140][141] , silicon 143 , germanium telluride 16 and strontium titanate 97,138 . The straight line corresponds to the weak coupling BCS ratio.…”

Section: Summarizing Remarksmentioning

confidence: 99%

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Superconductivity in doped semiconductors

Bustarret

2015

Physica C: Superconductivity and its Applications

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International audienceA historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike

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Section: D Superconducting Propertiesmentioning

confidence: 81%

Section: D Superconducting Propertiesmentioning

confidence: 99%

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Superconductivity in doped semiconductors

Bustarret

2015

Physica C: Superconductivity and its Applications

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“…Simultaneously, the reference potential with respect to the reference electrode was measured in order to precisely estimate the junction voltage V J . As the tunnel current is determined by the total number of electronic states which electrons can tunnel into, the differential tunneling conductance dI/dV encodes the energyresolved density of states (DOS) of FeSn overlaid onto a monotonic background signal arising from, e.g., energy-dependent DOS of the tunnel electrode [40][41][42][43][44][45][46] . We note that in the regime where the tunnel electrode has a small Fermi energy (i.e., E F,electrode < < |V J |) when V J < 0 the observed dI/dV is a direct measure of the intrinsic DOS spectrum (the case we will investigate primarily here); this is contrary to the case of V J > 0 where the absence of electronic states below the electrode's conduction band edge can make such a direct analysis more difficult (see Supplementary Note 23).…”

Section: Resultsmentioning

confidence: 99%

Evidence of two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn

et al. 2021

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The kagome lattice has long been regarded as a theoretical framework that connects lattice geometry to unusual singularities in electronic structure. Transition metal kagome compounds have been recently identified as a promising material platform to investigate the long-sought electronic flat band. Here we report the signature of a two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn by means of planar tunneling spectroscopy. Employing a Schottky heterointerface of FeSn and an n-type semiconductor Nb-doped SrTiO3, we observe an anomalous enhancement in tunneling conductance within a finite energy range of FeSn. Our first-principles calculations show this is consistent with a spin-polarized flat band localized at the ferromagnetic kagome layer at the Schottky interface. The spectroscopic capability to characterize the electronic structure of a kagome compound at a thin film heterointerface will provide a unique opportunity to probe flat band induced phenomena in an energy-resolved fashion with simultaneous electrical tuning of its properties. Furthermore, the exotic surface state discussed herein is expected to manifest as peculiar spin-orbit torque signals in heterostructure-based spintronic devices.

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“…This limit is appropriate, since via tunneling bulk doped STO is known to be in the weak-coupling regime [25]. The variation of H In the case of a 2D superconductor in a parallel magnetic field, if the sample is thin enough that orbital depairing is suppressed, spin paramagnetism is the dominant mechanism for destroying superconductivity [11].…”

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confidence: 99%

Intrinsic spin-orbit coupling in superconductingδ-doped SrTiO3heterostructures

et al. 2012

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We report the violation of the Pauli limit due to intrinsic spin-orbit coupling in SrTiO3 heterostructures. Via selective doping down to a few nanometers, a two-dimensional superconductor is formed, geometrically suppressing orbital pair-breaking. The spin-orbit scattering is exposed by the robust in-plane superconducting upper critical field, exceeding the Pauli limit by a factor of 4. Transport scattering times several orders of magnitude higher than for conventional thin film superconductors enables a new regime to be entered, where spin-orbit coupling effects arise nonperturbatively.Unconventional superconductivity is a subject of great theoretical and experimental interest [1][2][3]. A central issue in this field is the discovery and understanding of non-trivial pairing mechanisms, such as the spin-triplet Cooper pair, which has been explicitly investigated in heavy fermions [1], Sr 2 RuO 4 [4], and crystals with broken inversion symmetry [5]. Recently, novel pairing has also been predicted in two-dimensional systems breaking inversion symmetry [6, 7]. Experimentally, measurements of the superconducting upper critical field H c2 give vital information. In particular, violations of the Pauli paramagnetic limit [8,9] can be used to unravel the nature of the electron spins in the superconducting state. Notably, the presence of spin-orbit coupling (SOC) can be quantified [10], as demonstrated by the H c2 studies of metal thin-film superconductors [11] and bilayer systems where interface SOC drastically enhances H c2 [12].Electron-doped SrTiO 3 (STO) has attracted much attention as the lowest-density superconductor [13] with high-mobility [14]. These characteristics enable the creation of novel low dimensional systems [15], and are vital to shed light on the rich physics present at the LaAlO 3 /SrTiO 3 (LAO/STO) interface, where the presence of the Rashba spin-orbit interaction has been discussed, affecting both the normal and superconducting state transport properties [16,17]. However, despite the fact that the conduction band structure of STO is similar to p-type GaAs [18,19], the latter a model system for spintronics, the role of possible intrinsic SOC in the transport properties of doped STO is still unclear.In this Letter, we study the violation of the superconducting Pauli limit due to intrinsic SOC in a systematic series of symmetric, doped STO heterostructures. Using the δ-doping technique, we selectively add Nb dopants in a narrow region inside an otherwise continuous undoped STO host crystal. As the thickness of the dopant layer is reduced, the destruction of superconductivity by orbital pair-breaking is geometrically suppressed, and the superconducting H c2 is enhanced for magnetic fields applied parallel to the dopant plane. In the thin regime, when the dopant layer is just a few nanometers thick, the superconductivity is robust beyond the conventional Pauli limit, demonstrating the presence of spin-orbit scattering (SOS) in the STO. Moreover, due to the absence of a surface or interface close to the...

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Energy gap of the superconducting semiconductor SrTiO3−x determined by tunneling

Cited by 29 publications

References 17 publications

Superconductivity in doped semiconductors

Superconductivity in doped semiconductors

Evidence of two-dimensional flat band at the surface of antiferromagnetic kagome metal FeSn

Intrinsic spin-orbit coupling in superconductingδ-doped SrTiO3heterostructures

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